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31.
The Gondwana successions (1–4 km thick) of peninsular India accumulated in a number of discrete basins during Permo-Triassic period. The basins are typically bounded by faults that developed along Precambrian lineaments during deposition, as well as affected by intrabasinal faults indicating fault-controlled synsedimentary subsidence. The patterns of the intrabasinal faults and their relationships with the respective basin-bounding faults represent both extensional and strike-slip regimes. Field evidence suggests that preferential subsidence in locales of differently oriented discontinuities in the Precambrian basement led to development of Gondwana basins with varying, but mutually compatible, kinematics during a bulk motion, grossly along the present-day E–W direction. The kinematic disparity of the individual basins resulted due to different relative orientations of the basement discontinuities and is illustrated with the help of a simple sandbox model. The regional E–W motion was accommodated by strike-slip motion on the transcontinental fault in the north. 相似文献
32.
Sarbari Ghosh Utpal Kumar De Atmospheric Science Research Department of Physics Jadavpur University Calcutta India Received April revised July 《大气科学进展》1997,(1)
AComparativeStudyoftheAtmosphericLayersbelowFirstLiftingCondensationLevelforInstantaneousPre-MonsoonThunderstormOcurenceatAga... 相似文献
33.
Summary The rate of oceanic heat storage of the upper 200m of the Arabian Sea is explained in terms of net air-sea heat flux (Q
F), heat change due to horizontal divergence and vertical motion (Q
V) and heat change due to lateral advection (Q
A). The analysis revealed that the heat storage of the Arabian Sea is mainly controlled byQ
V while the effect ofQ
A is much larger than expected. Parameterisation of summer cooling revealed that the depletion of energy from the mixed layer is mainly due to upwelling and horizontal advection though large amount of heat is accumulated due to net air-sea heat flux. The annual heat balance of the upper 200m of the Arabian Sea suggested large heat gain by air-sea exchange processes. About two third of this heat gain is compensated by horizontal advection and one third by vertical advection.With 4 Figures 相似文献
34.
Santanu Kumar Bhowmik 《Journal of Earth System Science》1997,106(3):131-146
A suite of rocks from Borra Carbonate Granulite Complex (BCGC) in the Eastern Ghats granulite belt displays superposed structures
and overprinted mineral assemblages that reveal multiple episodes of tectonothermal reworking of the complex under granulite
facies condition. Five distinct episodes of deformation (D1, D2, D3, D4 and D5) and four phases of metamorphism (M1, M2, M3 and M4) are recorded. The signature of the earliest tectonothermal event, D1 is a gneissic foliation (S1) denned by segregation of peak granulite facies mineral assemblages corresponding to prograde M1 metamorphism. M2 metamorphic overprint represents an episode of near-isobaric cooling of the complex under a static condition. D2 represents an episode of ductile deformation manifested by isoclinal folding (F2) and associated extensional structures, within a broad framework of coaxial bulk deformation. The present study reveals that
D2 took place subsequent to M2 - Subsequent deformation, D3, produced F3 folds and also deformations of boudins formed during D2. M3, which is synchronous with F3, represents a near isothermal decompression of the BCGC. This was followed by a weak structural readjustment (D4), producing E-W cross folds. The latter was not, however, associated with any recognizable petrological reworking. In the
terminal events, deformation (D5) and mineral reactions (M4) were localized along narrow intersecting shear zones. The latter acted as channelways for carbonic and still later hydrous
fluid infiltration. The available thermobarometric data from BCGC and other areas of the Eastern Ghats belt reveal that reworking
during M2 and M3 ensued in a thermally perturbed regime. The high thermal regime might also have persisted during carbonic fluid infiltration
related to terminal reworking (M4). 相似文献
35.
36.
The electron cyclotron waves that originate at low altitudes (<0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions. 相似文献
37.
Geotechnical Properties of Low Calcium and High Calcium Fly Ash 总被引:1,自引:0,他引:1
In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian
fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical
and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture
content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional
and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant
effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash
is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase. 相似文献
38.
Sushina nepheline syenite gneisses of Early Proterozoic North Singhbhum Mobile Belt (NSMB), eastern India suffered regional metamorphism under greenschist-amphibolite transitional facies condition. The Agpaitic Sushina nepheline syenite gneisses consist of albite, K-feldspar, nepheline (close to Morozewicz-Buerger composition), aegirine, biotite, epidote, piemontite, sodalite, cancrinite, natrolite and local alkali amphibole. Accessory phases include zircon, hematite, magnetite, rare pyrochlore and occasional eudialyte and manganoan calcic zirconosilicates. Mineral chemistry of albite, K-feldspar, nepheline, aegirine, alkali amphibole, natrolite and zirconium silicate minerals are described. The detailed textural features together with chemical data of some minerals indicate metamorphic overprint of these rocks. A new reaction is given for the genesis of metamorphic epidote. Metamorphic piemontite suggests greenschist facies metamorphism under high fO2 (Hematite-Magnetite buffer). Up to 15.34 mol% of jadeite component in aegirine suggests that the metamorphic grade of the nepheline syenite gneiss reached at least to greenschist-amphibolite transitional facies or higher. Nepheline geothermometry suggests temperature of metamorphism <500 °C, which is consistent with greenschist facies metamorphism of surrounding chlorite-biotite-garnet phyllite country rock. 相似文献
39.
The use of suspensions of nanoparticles of titanium dioxide in photocatalytic degradation of dye solution has disadvantages of inconvenient separation of fine particles for reuse and limited penetration of light for effective degradation. These problems can be minimized by supporting titanium dioxide on various inert supports. The present study involves the preparation of immobilized titanium dioxide films by three different techniques and characterization of the prepared films. The immobilized films of nanocrystals of titanium dioxide were prepared using sol?Cgel technique, polyvinyl alcohol?Cformaldehyde binder and acrylic emulsion. The photocatalytic performance of the prepared films for degradation of amaranth dye has also been evaluated and compared. Combination of photodegradation and adsorption processes induces strong beneficial effects on removal of dyes. Addition of high adsorption capacity activated carbon to photoactive titanium dioxide in photodegradation of dyes improves the efficiency of dye mineralization. The activated carbon has also been immobilized along with titanium dioxide in the present work to examine the dual effect of photodegradation and adsorption in the removal of amaranth. The films formed with the help of polyvinyl alcohol?Cformaldehyde binder showed better dye degradation capabilities. 相似文献
40.
Prasanta Kumar Nayak Birendra Kumar Mohapatra Prem Prakash Singh 《Resource Geology》2014,64(4):387-394
Banded iron formation (BIF) of the Gorumahisani–Sulaipat–Badampahar (GSB) belt in Singhbhum Craton, India, consists predominantly of magnetite. This BIF is intruded by a magnetite dyke. The magnetite dyke is massive and compact with minor sulphide minerals while the host banded magnetite ore, a component of the BIF, shows thin lamination. The magnetite ore of the dyke is fine to medium grained and exhibits interlocking texture with sharp grain boundaries, which is different from the banded magnetite that is medium to coarse grained and show irregular martitised and goethitised grain boundaries. Relics of Fe–Ca–Mn–Mg‐carbonate and iron silicates (grunerite and cummingtonite) are observed in the banded magnetite. The intrusive magnetite is distinctly different in minor, trace and REE geochemistry from the banded magnetite. The banded magnetite contains higher amounts of Si, Al, Mn, Ca, Mg, Sc, Ga, Nb, Zr, Hf, Co, Rb and Cu. In contrast, the massive magnetite is enriched in Cr, Zn, V, Ni, Sr, Pb, Y, Ta, Cs and U with higher abundance of HREE. In the chondrite normalized plot, the massive magnetite shows a slight positive Eu anomaly while the banded ore does not show any Eu anomaly. Field disposition, morphology, mineralogy and chemistry show that the intrusive magnetite dyke is of igneous origin, while magnetite in BIF formed from a carbonate protolith through the process of sedimentation. 相似文献